JPA实现“一对多”映射

青旅半醒 2021-07-24 22:20 412阅读 0赞

**一 代码位置**

[https://gitee.com/cakin24/code/tree/master/08/JpaOneToManyDemo][https_gitee.com_cakin24_code_tree_master_08_JpaOneToManyDemo]

**二 关键代码**

1 School

package com.example.demo.entity;
    
    import lombok.Data;
    import javax.persistence.*;
    import java.util.List;
    
    @Entity
    @Data
    public class School {
        @Id
        @GeneratedValue(strategy = GenerationType.IDENTITY)
        private long id;
        private String name;
        //@OneToMany(cascade = CascadeType.ALL)
        @OneToMany()
        @JoinColumn(name = "school_id")
        private List<Teacher> teacherList;
    }

2 Teacher

package com.example.demo.entity;
    
    import lombok.Data;
    import javax.persistence.*;
    
    @Data
    @Entity
    public class Teacher {
        @Id
        @GeneratedValue(strategy = GenerationType.IDENTITY)
        private long id;
        private String name;
        @ManyToOne
        private School school;
    }

3 测试代码

package com.example.demo.entity;
    
    import com.example.demo.repository.SchoolRepository;
    import com.example.demo.repository.TeacherRepository;
    import org.junit.Test;
    import org.junit.runner.RunWith;
    import org.springframework.beans.factory.annotation.Autowired;
    import org.springframework.boot.test.context.SpringBootTest;
    import org.springframework.test.context.junit4.SpringRunner;
    import java.util.List;
    
    @SpringBootTest
    @RunWith(SpringRunner.class)
    public class OneToManyTest {
        @Autowired
        private SchoolRepository schoolRepository;
        @Autowired
        private TeacherRepository teacherRepository;
    
        @Test
        public void add() {
            School school1 = new School();
            school1.setName("清华大学");
            schoolRepository.save(school1);
            Teacher teacher = new Teacher();
            teacher.setName("long");
            teacher.setSchool(school1);
            teacherRepository.save(teacher);
        }
    
        @Test
        public void find() {
            School school1 = new School();
            school1 = schoolRepository.findSchoolById(1);
            List<Teacher> teacherList = school1.getTeacherList();
            System.out.println(school1.getName());
            for (Teacher teacher : teacherList) {
                System.out.println(teacher.getName());
            }
        }
    
        @Test
        public void deleteSchoolById() {
            schoolRepository.deleteById(1);
        }
    
        @Test
        public void deleteTeacherById() {
            teacherRepository.deleteById(1);
        }
    }

**三 测试**

1 运行第一个Test

控制台输出：

Hibernate: create table school (id bigint not null auto_increment, name varchar(255), primary key (id)) engine=InnoDB
    Hibernate: create table teacher (id bigint not null auto_increment, name varchar(255), school_id bigint, primary key (id)) engine=InnoDB
    Hibernate: alter table teacher add constraint FKrg46bnmgbcccayv14naymqg3r foreign key (school_id) references school (id)
    2020-01-02 10:30:52.397  INFO 796 --- [           main] j.LocalContainerEntityManagerFactoryBean : Initialized JPA EntityManagerFactory for persistence unit 'default'
    2020-01-02 10:30:53.222  INFO 796 --- [           main] com.example.demo.entity.OneToManyTest    : Started OneToManyTest in 7.666 seconds (JVM running for 9.233)
    Hibernate: insert into school (name) values (?)
    Hibernate: insert into teacher (name, school_id) values (?, ?)

数据库如下

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2NoZW5ncWl1bWluZw_size_16_color_FFFFFF_t_70][]

2 运行第二个Test

控制台输出：

Hibernate: select school0_.id as id1_0_, school0_.name as name2_0_ from school school0_ where school0_.id=?
    清华大学
    Hibernate: select teacherlis0_.school_id as school_i3_1_0_, teacherlis0_.id as id1_1_0_, teacherlis0_.id as id1_1_1_, teacherlis0_.name as name2_1_1_, teacherlis0_.school_id as school_i3_1_1_ from teacher teacherlis0_ where teacherlis0_.school_id=?
    Hibernate: select school0_.id as id1_0_0_, school0_.name as name2_0_0_ from school school0_ where school0_.id=?
    long

3 运行第三个Test

控制台输出：

Hibernate: select school0_.id as id1_0_0_, school0_.name as name2_0_0_ from school school0_ where school0_.id=?
    Hibernate: update teacher set school_id=null where school_id=?
    Hibernate: delete from school where id=?

数据库输出：

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2NoZW5ncWl1bWluZw_size_16_color_FFFFFF_t_70 1][]

4 运行第四个Test

控制台输出：

Hibernate: select teacher0_.id as id1_1_0_, teacher0_.name as name2_1_0_, teacher0_.school_id as school_i3_1_0_, school1_.id as id1_0_1_, school1_.name as name2_0_1_ from teacher teacher0_ left outer join school school1_ on teacher0_.school_id=school1_.id where teacher0_.id=?
    Hibernate: delete from teacher where id=?

数据库输出：

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2NoZW5ncWl1bWluZw_size_16_color_FFFFFF_t_70 2][]

[https_gitee.com_cakin24_code_tree_master_08_JpaOneToManyDemo]: https://gitee.com/cakin24/code/tree/master/08/JpaOneToManyDemo
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